Many alternate fuel vehicles, such as buses typically use fuels such as compressed natural gas (CNG), liquefied natural gas (LNG), or hydrogen fuel stored in relatively large fuel cylinders, to supply fuel for normal operation. The fuel cylinders are mounted to the frame of the vehicle and, particularly in the case of low floor buses, are mounted to the roof frame.
A challenge is thus presented to the bus manufacturer to attach the roof structure over the bank of cylinders and ensure that the roof is adequately secured to meet safety regulations. Due to the weight and overall dimensions, the roof is typically lifted by crane or other lifting device and placed on top of the frame, over the cylinders. If composite cylinders are used, the roof must be supported above the cylinders to prevent abrasion which may, over time, reduce the structural integrity of the cylinders.
Once positioned on the frame, the roof must be secured, the problem being that access is only available from the outside of the roof. Also problematic is the fact that predrilled holes in the roof carrying fasteners may not align perfectly with whatever receiving means is present on the frame. This can necessitate moving the large and unwieldy roof structure without damaging the roof or the underlying frame or cylinders or re-drilling holes so as to match the receiving means, which may mar the appearance of the roof.
U.S. Pat. No. 6,412,588 to Scott et al. teaches a roof or lid, formed in two pieces and attached at either end to the bus frame using hinges. The roof is supported, at the center where the two pieces join, by a post rising from the tank support. Systems, such as that taught by Scott, are complex and require moving parts, hinges, cables and the like. Further, should the roof be misaligned, gaps or overlap may result which spoil the aesthetics of the vehicle roof and may allow dirt and the like to enter the cylinder storage compartment.
Japanese patent JP 2000-225855 teaches a roof supported at either end by a triangular frame structure attached to the bus frame and at the periphery to the cylinder mounting frame. The addition of frame structures to support the roof adds considerably to the weight that must be supported on the bus frame.
Ideally, what is required is a lightweight system for mounting a roof to a frame of a vehicle. More particularly, the mounting system should be operable without access to the underside of the roof and should be adjustable to permit proper alignment of the roof with the frame.